Mechanical Image Reproduction
Nature-printing relied on simple physics. When an object, like a leaf or piece of lace was placed between a steel plate and a lead plate, and subsequently squeezed under tremendous pressure, the lead plate took an exact impression from the object. A replica of the lead plate with its sunken image was then made in copper via the electrotype process. After the image area was carefully filled with a pigmented gelatin ink, the plate could be printed on a conventional intaglio press. The resultant printed image was startlingly realistic, reproducing the most minute details of the original in absolutely smooth continuous tones. The effect was greatly enhanced by the fact that the printed image sat on the surface of the paper, so that it appeared as though the original object itself laid there. When multi-colored images were required, the appropriate gelatin inks were applied to the plate a la poupeé, and it was then printed as before.
A number of very beautiful nature-printed illustrations were produced during the 1850s and ‘60s by Auer and his English rivals William and Henry Bradbury, but with the discovery of more efficient photo-mechanical processes, this labor-intensive method soon disappeared from view.